This invention relates, in general, to the field of wired digital control network systems. In particular, this invention relates to a wired communication and control network system and a method for avoiding collision in the transmission of data in such a system.
Home and building automation is an important area in the development of modern technology, of which the design of control systems is one of its crucial areas. Many proposals have been put forward in this field, e.g. xe2x80x9cX-10xe2x80x9d, xe2x80x9cLonworkxe2x80x9d, xe2x80x9cCEBusxe2x80x9d and xe2x80x9cEIBxe2x80x9d.
Home and building control systems are complicated and multi-faceted systems. Stand-alone or point-to-point products clearly cannot fulfill the various requirements which may arise in real life situation. A control network system is much more versatile and may therefore meet such requirements. The nodes in such a control network system can communicate with one another, share the same resources, and be assembled together by various means (e.g. switches, sensors, timers, telephones, computers, etc.) in the light of the needs, in order to realize various control functions, e.g. integrated control and monitoring of lighting, energy, access and security at home or office.
Centralized control system is a well-known technology. However, the application of such a technology in home and building automation has met with various problems, e.g. complicated wiring (due to the large number of wires required), difficulty in extending the system (as there is usually a fixed capacity for each central control system), space requirement (due to the need to accommodate the central unit usually in a separate room), and the rigorous requirements for reliability (e.g. the whole system will not function when there are problems with the central unit).
At present, there are many media access control (MAC) methods, e.g. token passing, polling, circuit switching, and time-division multiple access (TDMA), etc. However, to a control network, while the signals/data to be transmitted arc usually relatively short, the response speed is required to be relatively high. Random access is thus one of the few methods which can meet the requirements of a real-time control.
In a random access system, it is possible that more than one node seek to transmit signals/data at the same time, resulting in a collision. Various methods have been devised to resolve such contentions, to recover from collisions, or to avoid collisions. Such methods include CSMA/CD (Carry Sense Multiple Access with Collision Detection) and CSMA/CA (Carry Sense Multiple Access with Collision Avoidance). However, irrespective of the method used, if two or more nodes transmit signals/data at the same time, all such attempted transmissions will fail. Each of these nodes has to stop transmitting for a respective period of time, and tries transmitting again. Such will cause a reduction of the communication efficiency.
Most current communication networks do not consider the issue of priority. If the data packets to be transmitted are not queued sequentially, each has to wait for the same pre-determined period of time before it is transmitted. This is a conventional method for, and does not cause much difficulty to, a communication system. However, the issue of priority becomes very important to a control system. The difference could be very significant since different nodes may carry out different functions within the system. In case of emergency, serious problems may arise if certain important signals/data cannot be transmitted by a particular node.
To a wired control network, it is desirable to keep the number of wires to a minimum. The more are the number of wires, the more inconvenient the wiring process will be, and the higher the risk of mis-wiring will also be. For example, even in a network in which there are only four wires (e.g. USB), there are 23 (i.e. (4!-1)) ways of mis-wiring.
While it is a common practice to provide a separate power source for each node in the network, it is desirable to provide electric power to the nodes through the network. Common link power systems generally adopt transformer coupling to separate power from signals in the bus/transmission medium. Because of the use of transformers, the system is usually of a relatively large size, and thus more expensive. In addition, due to the relatively low internal resistance of the transformer, the fanning-out capacity of the bus/transmission medium will be lowered when the transformer is connected to the network.
It is thus an object of the present invention to provide, a mixed mode transceiver digital control network system, a transceiver, a method of setting priority to each node, and a method for avoiding collision in such a system, in which the aforesaid shortcomings are mitigated, or at least to provide a useful alternative to the public.
According to a first aspect of the present invention, there is provided a digital data communication network system including a power supply means and at least two nodes, wherein said power supply means and said nodes are connected to one another via a transmission media whereby-digital signals/data are transmittable between said nodes, wherein said power supply means supplies electric power to said nodes, and wherein at least one of said nodes includes a current mode transmitter and at least one of said nodes includes a voltage mode receiver. This aspect of the invention has a number of independent sub-aspects. In one sub-aspect the system includes a pulse generating means through which electric current from said power supply means passes to induce a voltage pulse. In another sub-aspect the voltage mode receiver includes a capacitor and an inverter means.
According to a second aspect of the present invention, there is provided a digital data communication system for delivering digital signals from a current mode transmitter to a voltage mode receiver, said system including an electrically conductive cable coupling said transmitter and said receiver with each other, thereby providing a digital data communications path; DC power supply means for producing a pre-determined electric potential, said power supply means having a first voltage terminal and a second voltage terminal; current control means coupling said first voltage terminal of said power supply means to said cable for providing a first electric current path, said first electric current path operating as a low impedance path for DC current; voltage control means connected in parallel with said current control means for controlling the voltage amplitude across said current control means, and for providing a second electrical path for transient electric current; connecting means coupling said second voltage terminal of said power supply means to said cable to provide a power distribution path; wherein said current mode transmitter is coupled to said cable for implementing a current loop, wherein said transmitter produces current pulses in said current loop to perform a current mode digital data transmission; and wherein said voltage mode receiver is coupled to said cable for receiving voltage pulses on said cable produced by said voltage control means to perform a voltage mode digital data reception.
According to a third aspect of the present invention, there is provided a digital data communication network system for distributing power and for providing signal passing capabilities through a bus, said network including a plurality of nodes each including a mixed mode data bus transceiver for generating electric current pulses and receiving electric voltage pulses; an electrically conductive cable coupling said nodes with one another to provide a path for power delivery and data communications; a DC power supply means for producing a pre-determined electric potential, said power supply means having a first voltage terminal and a second voltage terminal; current control means coupling said first voltage terminal of said power supply means to said cable for providing a first DC current low impedance path; voltage control means connected in parallel with said current control means for controlling the voltage amplitude across said current control means and providing a second current path for transient current; and connection means coupling said second voltage terminal of said power supply means to said conductive cable to provide a power distribution path.
According to a fourth aspect of the present invention, there is provided a transceiver adapted to transmit and receive digital signals on a data bus which delivers direct current power and digital data simultaneously, said transceiver including a bridge rectifier having two connection terminals adapted to provide a non-polarity interface with said bus, said rectifier further including a + terminal and a xe2x88x92 terminal; a current mode transmitter coupled to said + terminal and said xe2x88x92 terminal of said rectifier for implementing a current loop adapted to produce electric current pulses to said data bus to perform current mode data transmission; a voltage mode receiver coupled to said + terminal and said xe2x88x92 terminal of said rectifier, said receiver being adapted to receive electric voltage pulses on said data bus to perform voltage mode data reception; and a current coupling means coupled to said + terminal and said xe2x88x92 terminal of said rectifier, said current coupling means being adapted to provide a regulated direct current supply to said transmitter and said receiver and other means in said transceiver.
According to a fifth aspect of the present invention, there is provided a method of communication in a mixed mode communication and control network system, wherein said system includes at least a first node, a second node, a power supply means, and current to voltage converter means connected with one another via a bus, comprising the steps of (a) generating at least a first electric pulse by said first node; (b) transmitting said first electric pulse to said power supply means in the form of an electric current; (c) causing a first electric current from said power supply means to pass through said current to voltage converter means to induce at least a second electric pulse; and (d) transmitting said second electric pulse into said bus.
According to a sixth aspect of the present invention, there is provided a method for medium access control in a mixed mode communication and control network system, wherein said system includes at least a first node and a second node each being adapted to transmit signals into a bus via which said nodes are connected with each other, including the steps of (a) establishing a plurality of priority levels each with a corresponding different range of waiting time; (b) assigning one of said plurality of priority levels to each of said nodes; (c) said first node generating a waiting time on the basis of the priority level assigned thereto; (d) said first node checking whether said bus is free for transmission; (e) said first node checking whether the said waiting time has expired; (f) repeating steps (d) and (e) until the waiting time has expired; and (g) commencing transmission of a first data packet by said first node if said bus is free for transmission.
According to a seventh aspect of the present invention, there is provided a method of transmitting data in a mixed mode communication and control network system, wherein said system includes at least a first node and a second node each being adapted to transmit pulses into a bus via which said nodes are connected with each other, including the steps of (a) said first node causing a pulse of a first polarity to be transmitted into said bus; (b) said first node checking whether a pulse of said first polarity appears on said bus; and (c) finishing sending said pulse of said first polarity into said bus for the full period of pulse time-width if a pulse of said first polarity is detected on said bus in step (b).
According to an eighth aspect of the present invention, there is provided a method of transmitting at least one data packet for providing a collision-free communications in a mixed-mode multi-drop random access digital control network, wherein said network includes at least a first node and a second node each being adapted to transmit and receive data packets through a bus via which said nodes are connected with each other and constituting a wired-AND logic, wherein said data packet includes at least a logic high and a logic low to be transmitted into said bus, said method including the steps of:
(a) when said first node seeks to transmit said logic low into said bus, said first node;
(1) checks logic state from said bus;
(2) starts to transmit said logic low into said bus if said bus presents logic high in step (1) above;
(3) completes transmitting said logic low into said bus for the full period of the time-width of the said logic low; and
(b) when said first node seeks to transmit said logic high into said bus, said first node:
(1) starts to transmit said logic high into said bus;
(2) checks logic state from said bus;
(3) checks whether a pre-determined waiting time is up; and
(4) repeats steps (b)(2) and (b)(3) until said first node completes transmission of said logic high into said bus for the full period of the time-width of said logic high if said bus keep on presenting logic high in step (b)(2).
According to a ninth aspect of the present invention, there is provided a method of transmitting at least one data packet for providing a collision-free communications in a mixed-mode multi-drop random access digital control network, wherein said network includes at least a first node and a second node each being adapted to transmit and receive data packets through a bus via which said nodes are connected with each other and constituting a wired-OR logic, wherein said data packet includes at least a logic high and a logic low to be transmitted into said bus, said method including the steps of:
(a) when said first node seeks to transmit said logic high into said bus, said first node:
(1) checks logic state from said bus;
(2) starts to transmit said logic high into said bus if said bus presents logic low in step (1) above;
(3) completes transmitting said logic high into said bus for the full period of the time-width of the said logic high; and
(b) when said first node seeks to transmit said logic low into said bus, said first node:
(1) starts to transmit said logic low into said bus;
(2) checks logic state from said bus;
(3) checks whether a pre-determined waiting time is up; and
(4) repeats steps (b)(2) and (b)(3) until said first node completes transmission of said logic low into said bus for the full period of the time-width of said logic low if said bus keep on presenting logic low in step (b)(2).
According to a tenth aspect of the present invention, there is provided a transceiver adapted to transmit and receive digital signals/data via a mixed mode bus which delivers direct current power and digital data simultaneously, said transceiver including current mode transmitter means for implementing a current loop adapted to produce electric current pulses to said bus to perform a current mode data transmission, and voltage mode receiver means for receiving electric voltage pulses on said bus to perform voltage mode data reception. This aspect of the invention has a number of independent sub-aspects. In one sub-aspect the transceiver includes bridge rectifier means for providing a polarity insensitive interface with said bus. In another sub-aspect the transceiver includes current coupling means for providing a regulated direct current source. In yet another sub-aspect the receiver means includes an input capacitor and an inverter means.
Preferred embodiments of the invention will now be described by way of examples, and with reference to the accompanying drawings, in which:
FIG. 1 is a schematic diagram of a conventional voltage mode multi-drop network system;
FIG. 2 is a schematic diagram of a conventional current mode multi-drop network system;
FIG. 3 is a schematic diagram of a first mixed mode multi-drop network system according to the present invention;
FIG. 4 is a schematic block diagram of a first embodiment of an application system according to the present invention;
FIG. 5 is a schematic block diagram of a second embodiment of an application system according to the present invention;
FIG. 6 shows the current flow and the voltage change at certain points of the system when a negative pulse is transmitted into the bus and received by a receiver in the embodiment shown in FIG. 5;
FIG. 7 shows the current flow and the voltage change at certain points of the sytem when a positive pulse is transmitted into the bus and received by a receiver, after a negative pulse has just been transmitted into the bus in the embodiment shown in FIG. 5;
FIG. 8 shows the data frame format used in the system according to the present invention;
FIG. 9 shows the data bits format used in the system according to the present invention;
FIG. 10 shows the data packet format used in the system according to the present invention;
FIG. 11 is a table showing the respective waiting time of the priority levels;
FIG. 12 is a flowchart showing the process whereby a node initials a transmission;
FIG. 13 is a timing chart showing a method for access control and collision avoidance according to the present invention;
FIGS. 14 and 15 are flowcharts showing the back-off method for collision avoidance;
FIG. 16 is a schematic block diagram showing a four-node system according to the present invention, in which the four nodes attempt to transmit signals/data simultaneously;
FIGS. 17A to 17D show the respective waveform of the voltage at the output of the micro-controller of the four nodes in FIG. 16;
FIGS. 18A to 18D show the respective waveform of the sink current ia, ib, ic, and id of the four nodes in FIG. 16;
FIGS. 19A to 19D show the respective waveform of the voltage at the input of the micro-controller of the four nodes in FIG. 16;
FIG. 20 shows the waveform of the DC supply source current i of the system shown in FIG. 16;
FIG. 21 shows the waveform of the inductor source current il of the system shown in FIG. 16;
FIG. 22 shows the waveform of the current ip flowing through the bi-directional clamp of the system shown in FIG. 16;
FIG. 23 shows the waveform of the voltage vp across the bi-directional clamp of the system shown in FIG. 16;
FIG. 24 shows the waveform of the bus voltage v of the system shown in FIG. 16; and
FIG. 25 is a schematic diagram of a second mixed mode multi-drop network system according to the present invention.